In a digitally controlled inkjet printing system, a receiver media (also referred to as a print medium) is conveyed past a series of components. The receiver media can be a cut sheet of receiver media or a continuous web of receiver media. A web or cut sheet transport system physically moves the receiver media through the printing system. As the receiver media moves through the printing system, liquid (e.g., ink) is applied to the receiver media by one or more printheads through a process commonly referred to as jetting of the liquid. The jetting of liquid onto the receiver media introduces significant moisture content to the receiver media, particularly when the system is used to print multiple colors on a receiver media. Due to the added moisture content, an absorbent receiver media expands and contracts in a non-isotropic manner, often with significant hysteresis. The continual change of dimensional characteristics of the receiver media can adversely affect image quality. Although drying is used to remove moisture from the receiver media, drying can also cause changes in the dimensional characteristics of the receiver media that can also adversely affect image quality.
FIG. 1 illustrates a type of distortion of a receiver media 3 that can occur during an inkjet printing process. As the receiver media 3 absorbs the water-based inks applied to it, the receiver media 3 tends to expand. The receiver media 3 is advanced through the system in an in-track direction 4. The perpendicular direction, within the plane of the un-deformed receiver media 3, is commonly referred to as the cross-track direction 7. Typically, as the receiver media 3 expands in the cross-track direction 7, contact between the receiver media 3 and the contact surface 8 of the rollers 2 (or other web guiding components) in the inkjet printing system can produce sufficient friction such that the receiver media 3 is not free to slide in the cross-track direction 7. This can result in localized buckling of the receiver media 3 away from the rollers 2 to create lengthwise flutes 5, also called ripples or wrinkles, in the receiver media 3. Wrinkling of the receiver media 3 during the printing process can lead to permanent creases in the receiver media 3 which adversely affects image quality.
U.S. Pat. No. 8,079,694 to Daly et al., entitled “Clear Fluid Patterning on Paper Media,” discloses depositing clear toner surrounding the entirety of the image or images, and the clear toner covers all or, in one case, most of the page on which the image is printed. “The pattern of clear fluid is defined by a maximum width that is generally equal to the maximum width of the image to be formed,” (Abstract) and the clear fluid must “contact” the image it surrounds.
While U.S. Pat. No. 8,079,694 is satisfactory, it includes drawbacks. First, the present invention overcomes the limited teachings of U.S. Pat. No. 8,079,694 in which the maximum width of a pattern must be equal to the image to be formed. Second, this method is costly since clear fluid is deposited in large quantities on the page of interest. Costly is obviously a driver in deciding whether a method is suitable for commercial use. Therefore, a need exists for a means to prevent the formation of receiver media wrinkles as a receiver media contacts web-guiding structures in a digital printing system which is cost effective in the use of clear fluid and overcomes technical limitations of the prior art.
As will be described below, the present invention solves the shortcomings of U.S. Pat. No. 8,079,694.